COMPARISON OF SCHEIMPFLUG CAMERA IMAGING PATTERNS AND PARAMETERS OF PELLUCID MARGINAL DEGENERATION AND KERATOCONUS

Abstract

OBJECTIVE: This study aims to compare the topography patterns and parameters in eyes with pellucid marginal degeneration (PMD) and eyes with keratoconus (KC). MATERIAL AND METHODS: This study is a retrospective and comparative study. Twenty-nine eyes of 15 patients with PMD and 46 eyes of 25 patients with keratoconus (KC) underwent examination. Topographic patterns of axial curvature, anterior and posterior elevation maps, and pachymetric maps obtained by the Scheimpflug camera were categorized. RESULTS: In eyes with PMD, the crab-claw pattern (93.1% of all axial curvature map patterns) was the most prevalent. The most common patterns in eyes with KC were inferior (41.3%) and central (39.1%) steepening patterns. In eyes with PMD, the asymmetric island pattern (96.6%) was the most prevalent pattern in elevation maps. Asymmetric incomplete ridge pattern (54.3%), center island (17.4%), and asymmetric regular ridge pattern (15.2%) were the most common elevation map patterns in eyes with KC. Among pachymetric map patterns, the decentred oval pattern was most frequent in eyes with PMD, paracentral oval pattern (54.3%), and decentred round pattern (34.8%) in eyes with KC. The result of the receiver operating characteristics (ROC) graphs showed that the anterior and posterior asphericity (Q) values had the maximum area under the ROC curve (0.98 and 0.93 respectively) in discriminating PMD and KC. CONCLUSIONS: The crab-claw pattern for the axial curvature map, asymmetric island pattern for the anterior and posterior elevation map, and decentred oval pattern for the pachymetric map were frequently observed in eyes with PMD. Asphericity values of the cornea may be clinically relevant parameters for effectively discriminating PMD from KC.